1. Field of Invention
This invention relates generally to a system and method of planning, scheduling, and dispatching during wafer production in a Fab and, more particularly, to an automated decision engine that integrates short-term (dispatching) and long-term (scheduling) production plans for optimum dispatching and scheduling of wafer build throughout the wafer""s movement in the Fab.
2. Description of Related Art
In semiconductor manufacturing Fabs costing billions of dollars efficient use of tools is essential to controlling costs and maximizing throughput of the product. During the building of wafers, the wafer box or Front Open Unified Pot (FOUP) travels from position to position to be placed into the next required tool for its next processing to take place. A Fab planner does long-term production planning and calculates an optimal path using a scheduling tool. Separately, a Fab supervisor planner is doing short-term production planning to balance and filter WIP (Work in Progress) with a dispatching tool to set up an optimal path based on what is actually happening currently on the Fab floor. Setting up different rule for different product areas is usually done using a dispatching tool. As the planning is done differently and at different times, the plans are frequently inconsistent with effort sometimes being duplicated. Integrating of the two plans can be very difficult. Furthermore, individual usage of different reports by both the planner and supervisor can result in conflict between reports, subjectiveness, and increased costs due to software efforts needed to create support for this.
Most of the dispatching system has many exception rules, making it inefficient and very difficult to maintain. Furthermore, most dispatching systems do not consider the current position of the FOUP, so the optimal decision cannot be reached on the next move to make in a dynamic Fab like the new 300 mm Fab. In the more complex 300 mm Fabs, an Automatic Machine Handling System (AMHS) must choose the FOUP to be transferred by the dispatch system. As the AMHS is not rule based, it is difficult to modify rules or easily set up rules for each equipment type.
An additional difficulty comes from the fact that the scheduling tool has a performance issue, making it difficult for the supervisor to get real-time data from it. The bottom line is that current full-automation systems such as the 300 mm Fab with an AMHS can optimize MES logical data but can not optimize stocker utilization or avoid traffic jams caused by the AMFHS system.
A new method and system is needed to resolve these problems and optimize the FOUP travel through the Fab. This invention solves these problems and provides additional benefits.
In U.S. Pat. No. 5,880,960 (Lin et al.) a method to improve WIP balance in the manufacturing line is discussed. In U.S. Pat. No. 5,751,580 (Chi) a fuzzy logic method and system for adjusting of priority rating of work is discussed. In U.S. Pat. No. 5,623,413 (Matheson et al.) a scheduling system and method for moving objects through a multipath system is discussed. In U.S. Pat. No. 5,612,886 (Weng) a method and system for the dynamic dispatching of work in progress is discussed. In U.S. Pat. No. 5,548,518 (Dietrich et al.) an allocation method for generating a production schedule is discussed. In U.S. Pat. No. 5,546,326 (Tai et al.) a dynamic dispatching method is discussed. In U.S. Pat. No. 5,446,671 (Weaver et al.) a look-ahead method for maintaining optimum queued quantities is discussed. In U.S. Pat. No. 5,444,632 (Kline et al.) an apparatus and method for controlling and scheduling processing machines is discussed. In U.S. Pat. No. 5,229,948 (Wei et al.) a method of optimizing a serial manufacturing system is discussed.
This invention""s overall objective is to provide an integrated method and system for the automation of a semiconductor Fab for production decision support. More specifically, the objective is to provide for a software decision engine to supervise optimal throughput of product into processing equipment. It is also an objective that the decision engine be rule based and that it define and integrate with a cooperative model between dispatch and schedule functions. It is another objective to have other Fab systems also integrate with the decision engine to interact as a unified whole system.
Additionally, it is an objective to provide a decision evaluation formula to integrate the results of system analysis tools for production decision support. It is an objective to have a sub-formula of the decision evaluation formula to resolve dynamic constraint issues. It is also an objective for the method and system to provide for an automatic learning methodology.
These objectives are achieved by the method and system of this invention. The use of this method and system in a Fab system provides cost savings by efficient automation and by optimizing the throughput of product traveling from tool to tool. It reduces bottle necks and over and under supply to tools by allowing each tool equipment control program to help in the movement of product between tools.